Refractory gunning composition and method of producing the same



REFRACTORY GUNNING COMPOSITIONv AND METHOD OF PRODUCING THE Louis J.Jacobs, Chicago, Ill., assignor to The S. Obermayer Co, Chicago, 111., acorporation of Ohio No Drawing. Application June 11,1956

Serial No. 590,378

12 laims. (Cl. 106-67) This invention relates to refractory materialsfor use in monolithic construction work. More particularly, it relatesto a sc -called gunning mixture of such materials, that is, a mixture ofrefractory materials which is suitable for spraying from a'spray. gun toprovide a monolithic refractory construction of high quality andeconomy. V

The present application is a continuation-in-part of my co-pendingapplication Serial No. 385,033, filed on October 8, 1953, now abandoned,which was in turn a continuation-in-part of application Serial No.178,551, filed August 9, 1950, now abandoned.

The formulation of refractory materials is a diflicult problem, becauseattempts to improve a certain characteristic frequently result inaggravated defects in other characteristics. This problem isparticularly difficult of solution when the material is to be appliedthrough a spray gun.

Heretofore, materials of this type frequently failed to adhere whenprojected against a wall or the like. This is a condition which is knownas rebound and which results in the complete or partial loss of largequantities of refractory material. Also, even if such materials didadhere to the surface, they frequently failed to knit together properlyand to form a dense,non-porous coating. These materials also tended toshrink excessively upon the original firing of the refractory structureconstructed from them, thereby tending to induce cracking of refractorylinings or distortion of structures or both.

Another important problem encountered with prior materials is thatgunning of the mixture frequently could be continued without apparentdifiiculty for only about 15 to 20 minutes. Then, the spray nozzle wouldsuddenly clog. Such clogging was frequently so serious that a mere blastspray fluid was insufiicient to correct the situation, and the gun hadto be disassembled and cleaned.

Many attempts have been made to correct one or more of these defects.For example, in an attempt to decrease the amount of rebound the amountof water added at the spray nozzle was increased. However, by doingthis, the adhering refractory material was thereby made substantiallyless dense and had a substantially greater tendency to shrink and tocrack.

Binder materials, which are well known in this art, were added in anattempt to improve adhesion while not interfering with the knittingtogether of the structure. However, the clogging difiiculties in the gunwere increased.

it is an object of the instant invention to provide an improvedrefractory gunning composition.

It is a further object of the instant invention to provide a refractorygunning composition which adheres to the wall or target against which itis directed and knits together properiy to form a dense coating.

A still further object of the instant invention is to provide arefractory gunning composition which does not crack or shrinkexcessively, upon the firing of the monolithic structure which isformed.

' tct ice A further object of the instant invention is to provide. anon-agglomerating refractory gunning composition which does not clog thespray gun.

These and other objects of the invention will become more apparent fromthe description following.

The instant improved refractory gunning composition is a mixture ofindividual, non-agglomerated particles comprising coarse grains ofnon-plastic refractory coated first with sticky plastic bond clay andthen with a dry mixture of .bond clay and fine grains of non-plasticrefractory.

The novel method for producing the instant refractory involves twoseparate mixing steps. During the first step or mixing operation, coarserefractory particles are mixed with bond clay which has beenmoistened-with enough water to make the bond clay sticky. Preferably,wettingv of the bond clay is facilitated by using water containing awetting agent. Sufficient sticky bond clay is used to com pletely'coatthe coarse grains.

Generally, theratio byweight of bond clay and coarse grains in'the firstmixing step is between about 1:4 and about 1:15.

By the term coarse grains as used herein is meant clay particles havinga size between about 3 and about 30 mesh. I

The coarse refractory grains used in the instant invention arenon-plastic type clays, such as calcinedflint clay, i. e., a hardflint-like fireclay occurring as an unstratified massive rock,practically devoid of natural plas-= ticity and showing a conchoidalfracture.- Other nonplasic materials suitable'for use as the coarsefraction include calcined fireclay, pyrophyllite, silica or chrome ore.

The bond clay used is a plastic fireclay and is desig-' nated C-71-51 bythe American Society of Testing Materials, which in its Manual on ASTMStandards on Re fractory Materials (published by ASTM, Philadelphia,1952 edition) at page 130 defines a plastic fireclay as a fireclay ofsufficient natural plasticity to bond nonplasticmaterials. The bondclayused in the preparation of the instant gunning composition of theinvention is preferably the type mined in Kentucky and Ohio, and ispreferably ground to pass a 16 mesh sieve.

The wetting agent is mixed with the bond clayand, water in order tolower the surface tension of the water so it will moisten the bond clayfaster and'develop a maximum of stickiness with a minimum amount ofWater.

The example given below employs as the wetting agent the productSantomerse S (an alkylated aryl sulfonate) manufactured and sold by theMonsanto Chemical Company. However, itisobvious to anyone skilled in theart that other surface active wetting agents can be used.

The amount of water used in this step obviously varies with thecharacteristics of the particular bond clay. However, the amount ofwater used should be no more. than that sufficient to moisten the bondclay and make it sticky and plastic.

The coarse grains are mixed with the sticky bond clay until completelycoated therewith. The length of time necessary-for this mixing dependsupon the efficiency of the mixer. However, with most heavy muller typemixers, the step is complete within about 5 to about non-sticky, the drybond clay is used to produce material which will not agglomerate. Thefine grains are bond clay-coated coarse.

In this step in which the. surface of the coated sticky coarse grainsare rendered used in this step to reduce the drying and firing shrinkageof the product.

The fine grains used are of a non-plastic clay, such as a calcinedfireclay, or pyrophyllite, or silica, or chrome ore.

The particle size of the fine grain refractory should always be smallerthan mesh but varies, and the size of the fine grains depends upon thesize of the particles in the coarse grain fraction. The fine grains arepreferably of such size as to pass through a sieve at least about 10mesh sizes smaller than the mesh size of the smallest of the particlesin the coarse grain fraction. For example, if the clay particles of thecoarse fraction have a mesh size between about 3 to about mesh, the finegrains should all be smaller than about mesh. But when the mesh size ofthe coarse grains is between about 3 to about 10 mesh, the fine grainsare preferably at least smaller than about 20 mesh. In the preferredembodiment the ratio by weight of the amount of coarse grains used inthe primary coating step to the amount of fine grains used in thesecondary coating is between about 2:1 and about 4:1.

In the second mixing step, the quantity by weight of fine grains issubstantially less than the quantity by weight of coarse grains used inthe first step. The ratio by weight of fine grains to coarse grains isbetween about 1:2 and about 1:4. However, the number of particles offine grains is substantially greater than the number of coarse grains.

The amount by weight of bond clay added with the fine clay particles inthe second step is substantially greater than employed in the primarymixing step. Generally the ratio by weight of bond clay used in thefirst and second mixing steps is between about 1:15 and about 1:5.

In the second step, if an amount of bond clay less than the lower limitof the above range is employed, the coating of the coarse grains isinsufiicient, and agglomeration and jamming of the composition in thespray gun may occur. If an amount of bond clay greater than the upperlimit is used, excessive shrinkage of the completed structure willoccur.

Theoretically,it might be considered necessary to have a relativelylarge quantity of bond clay for the relatively heavy weight of coarsegrains. In practice, I have found that this is not so; and that, on thecontrary, it is a feature of the instant process that by far the greaterquantity by weight of bond clay is admixed only in a second step,wherein the fine flint clay is mixed with the precoated coarseparticles.

The gunning compositions obtained by the instant process have thefollowing compositional limits by weight:

In the instant composition the ratio of the total refractory grains toplastic bond clay used should be within the range of 2:1 to 4:1. If theratio of refractory grains to plastic bond clay exceeds about 4:1, theresulting mixture will not agglomerate properly when sprayed, andcracking will occur in the completed monolithic structure. If the ratioof refractory grains to plastic bond clay is less than about 2:1, thecompleted monolithic structure will have insufficient strength andexcessive shrinkage will occur. In addition, jamming in the spray gunmay occur.

While the wetting agent is not indispensable, it is preferable to useit, because it results in more rapid and thorough moistening of the bondclay, together with increased plasticity thereof, and a generallysuperior final product. Ordinarily from 0.03% to 0.15% dry solidswetting agent is sufiicient, computed on the total weight of the gunningcomposition. A larger quantity of wetting agent is usually useless andof course is economically undesirable.

If desired, it is also possible to add other materials to thecomposition. For example, a binding agent, such as lignin sulfonate, canbe added to the first or second mix, in accordance with a practicefrequently used in this art. However, only a small amount should beused. Although the binder improves the anti-rebound and similarfunctions slightly, it has often been found to lead to difficulties inconnection with the clogging of the gun. In practicing the instantinvention, it is preferred to omit binding agents.

The ingredients contained in the ultimate product are those employed inthe two successive steps of the manufacturing procedure; the compositionbeing a purely physical mixture of he different sizes of non-plasticparticles, the bond clay, absorbed water, and the wetting agent. Thephysical form and condition of the material and of the particles thereofare different from those previously known in gunning compositions.

As indicated above, an easily recognizable feature of the newcomposition is that it substantially consists of an aggregate ofseparate non-agglomerated particles. Each of these separate particleshas an inner grain of coarse non-plastic clay and an individual coatingof bond clay admixed with fine grains of non-plastic clay. It is thisseparate and individual character of the particles which allows forsmooth and efiicient gunning and the ultimate formation of a propermonolithic mass.

The particles produced by the two-step mixing process are substantiallyfree from any tendency to agglomerate I with one another while beingstored in the normal manner. The strong impact caused by spraying isnecessary to cause the ultimate cohesion and agglomeration of the mass.rangement of flint clay and bond clay, wherein the fine flint claygrains are embedded in thin, coherent layers of bond clay between thecoarse flint clay grains.

To more clearly illustrate the character of the instant invention, butwith no intention to be limited thereto, the following example is given:

EXAMPLE I Eight separate batches of refractory gunning composition wereprepared using the quantities of the materials shown in Tables I and IIbelow:

Table I I II III IV V VI VII VIII Coarse grains, pounds..- 560 560 560500 500 750 400 500 Bond clay, pounds 50 50 100 50 100 100 Wetting agent30% solids content, pints 3 3 3 8 3 1 2 2 Water gallons 1 1% 1% 1 1% 1 22 Table II I II III IV V VI VII VIII Fine grains, pounds... 190 190 190300 200 100 300 Bone clay, pounds 200 150 150 200 100 200 w 250 Table Igives the quantity of materials used in the primary mixing step. In thisstep, comminuted calcined flint clay, having a size between 3 and 10mesh, was mixed with plastic bonding fireclay, ground to pass a 16 meshsize sieve, water, and wetting agent (Santomerse S), for about 7minutes. This mixing produced masses of coarse particles completelycoated with a sticky layer of bond clay.

Table II shows the amount of the materials used for the respectivebatches in the secondary mixing step. In this step, the sticky grainsproduced in the first step were mixed for about two minutes with anadditional quantity This impact does not interfere with the ideal ar-.

of bond clay and with calcined fiintclay comminuted to a size smallerthan 20 mesh.

Thus, it will be seen that the process comprises first, a relativelylong mixing operation for the heavy mass of coarse grains together witha relatively small amount of bond clay, water, and wetting agent; andsecond, a relatively short mixing operation for the resulting coatedgrains with the fine grains and relatively large amount of bond clay.

Table HI shows the percentages by weight of the total plastic bond clay,the coarse fraction and the fine fraction of non-plastic clay grains inthe above gunning compositions.

T ble III I II III IV V VI VI VIII Coarse grains (percent) 56 56 56 5050 '75 40 50 Flne grains (percent) 19 19 19 30 20 30 Bond clay (percent)25 25 25 80 15 30 35 grains of refractory clay, between about 10% andabout by weight of fine grains of refractory clay, between about 15% andabout 35% by weight of bond clay, up to about 0.5% by weight of wettingagent, and a small amount of water, and wherein each coarse grain has aprimary coating of moistened bond clay and an exterior coating of 'drybond clay and said fine grains.

2. The product of claim 1 wherein the coarse grains are between about 3and about 10 mesh size, and substantially all of the fine grains aresmaller than about 20 mesh.

3. A method for producing a non-agglomerated refractory compositionwhich comprises coating coarse grains of refractory material withplastic bond clay moistened with water and a wetting agent, therebyproducing coarse grain having a sticky coating of the clay, and coatingsaid sticky coarse grains with a dry mixture of fine grains ofrefractory material and plastic bond clay.

4. The method as described in claim 3 wherein the ratio by weight ofplastic bond clay employed in the first and in the second mixing stepsis between about 1:1.5 and about 1:5.

5. The method as described in claim 3 wherein the ratio by weight ofcoarse grains to fine grains is between about 2:1 and about 4:1.

6. A method for producing a refractory composition which comprisescoating an aggregate of coarse grains of refractory material withplastic bond clay moistened with water and wetting agent to producea'primary sticky coating, and coating the particles in the resultingmass with a dry mixture of plastic bond clay and fine refractory grains,the ratios by weight employed of coarse to fine grains and of refractorygrains to bond clay being both between about 2:1 and about 4:1, and theratio by weight of bond clay used in the primary and in the secondarycoatings being between about 1:1.5 and about 1:5.

7. A refractory composition consisting essentially of between about 40%and about 78% by weight of coarse grains of refractory clay, betweenabout 10% and about 35 by weight of fine grains of refractory clay,between about 15 and about 35% by weight of bond clay, and a smallamount of water, and wherein each coarse grain has a primary coating ofmoistened bond clay and an exterior coating of dry bond clay and saidfine grains.

8. A refractory composition consisting essentially of an aggregate ofcoarse grains of refractory material, each of said grains having aprimary coating of moistened plastic bond clay, and an exterior coatingof dry bond clay and fine grains of refractory material, and wherein theratio by weight of coarse to fine grains is between about 2:1 and about4:1, and the ratio by weight of refractory grains to bond clay isbetween about 2:1 and about 4:1.

9. A method for producing a non-agglomerated refractory compositionwhich comprises coating coarse grains of refractory material withmoistened plastic bond clay, thereby producing coarse grains having asticky coating of the clay, and coating said sticky coarse grains with adry mixture of fine grains of refractory material and plastic bond clay,the ratio by weight of refractory grains to plastic bond clay beingbetween about 2:1 and about 4:1.

10. A refractory composition consisting essentially of about by weightdry solids of coarse grains of re fractory clay, about 20% by weight drysolids of fine grains of refractory clay, and about 25% by weight drybond clay, wherein the coarse grains are covered with a primary coatingof moistened bond clay and an exterior coating of dry bond clay and saidfine grains.

11. A method for producing a non-agglomerated refractory compositionwhich comprises coating coarse grains of refractory material withplastic bond clay moistened with water and a wetting agent, therebyproducing coarse grains having a sticky coating of said clay, andcoating the sticky coarse grains thus formed with a dry mixtureconsisting essentially of plastic bond clay and fine grains ofrefractory material.

12. A refractory composition consisting essentially of between about 40%and about 78% by weight refractory clay in coarse grains, between about10% and about 35% by weight of refractory clay in fine grains, betweenabout 15% and about 35 by weight of bond clay, up to about 0.5% byweight of wetting agent, and a small amount of water, and whereinsubstantially all of the coarse grains of refractory clay have a primarycoating of moistened bond clay and an exterior coating consistingessentially of dry bond clay and said fine grains of refractory clay.

References Cited in the file of this patent UNITED STATES PATENTS2,425,152 Greger et al. Aug. 5, 1947 2,460,268 Kauffman et al Feb. 1,1949 2,543,548 Henry Feb. 27, 1951

1. A REFRACTORY COMPOSITION CONSISTING ESSENTIALLY OF BETWEEN ABOUT 40%AND ABOUT 78% BY WEIGHT OF COARSE GRAINS OF REFRACTORY CLAY, BETWEENABOUT 10% AND ABOUT 35% BY WEIGHT OF FINE GRAINS OF REFRACTORY CLAY,BETWEEN ABOUT 15% AND ABOUT 35% BY WEIGHT OF BOND CLAY, UP TO ABOUT 0.5%BY WEIGHT OF WETTING AGENT, AND A SMALL AMOUNT OF WATER, AND WHEREINEACH COARSE GRAIN HAS A PRIMARY COATING OF MOISTENED BOND CLAY AND ANEXTERIOR COATING OF DRY BOND CLAY AND SAID FINE GRAINS.